Image sensing device with grid structure and fabrication method thereof

ABSTRACT

The present disclosure provides an optical structure and a method for fabricating an optical structure, the method includes forming a light detection region in a substrate, forming an isolation structure at surrounding the light detection region, and forming a primary grid over the isolation structure, including forming a metal layer over the isolation structure, forming a first dielectric layer over the metal layer, and partially removing the metal layer and the first dielectric layer with a first mask by patterning, and forming a secondary grid at least partially surrounded by the primary grid laterally.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 16/414,498, filed May 16, 2019, which claims the benefit of thereofunder 35 U.S.C. 120.

BACKGROUND

Digital cameras and other optical imaging devices often employ opticalstructures such as semiconductor image sensors. Optical structures canbe used to sense radiation and may convert optical images to digitaldata that may be represented as digital images. For example,complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) andcharge-coupled device (CCD) sensors are widely used in variousapplications such as digital camera, mobile phone, detector, or thelike. The optical structures utilize light detection regions to senselight, wherein the light detection regions may include pixel array,illumination image sensor (such as back side illumination image sensor,which can be referred to as BSI image sensor), or other type of imagesensor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a cross sectional view of an optical structure, according tosome embodiments of present disclosure.

FIG. 1B is a cross sectional view of an optical structure, according tosome embodiments of present disclosure.

FIG. 1C is a cross sectional view of an optical structure, according tosome embodiments of present disclosure.

FIG. 2A is a top view perspective of an optical structure, according tosome embodiments of present disclosure.

FIG. 2B is a top view perspective of an optical structure, according tosome embodiments of present disclosure.

FIG. 3A shows a flow chart representing a method for fabricating anoptical structure, in accordance with some embodiments of the presentdisclosure.

FIG. 3B shows a flow chart representing a method for fabricating anoptical structure, in accordance with some embodiments of the presentdisclosure.

FIG. 4 to FIG. 14 are cross sectional views of an optical structureduring intermediate stages of manufacturing operations, according tosome embodiments of present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the terms“substantially,” “approximately,” or “about” generally means within avalue or range which can be contemplated by people having ordinary skillin the art. Alternatively, the terms “substantially,” “approximately,”or “about” means within an acceptable standard error of the mean whenconsidered by one of ordinary skill in the art. People having ordinaryskill in the art can understand that the acceptable standard error mayvary according to different technologies. Other than in theoperating/working examples, or unless otherwise expressly specified, allof the numerical ranges, amounts, values and percentages such as thosefor quantities of materials, durations of times, temperatures, operatingconditions, ratios of amounts, and the likes thereof disclosed hereinshould be understood as modified in all instances by the terms“substantially,” “approximately,” or “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thepresent disclosure and attached claims are approximations that can varyas desired. At the very least, each numerical parameter should at leastbe construed in light of the number of reported significant digits andby applying ordinary rounding techniques. Ranges can be expressed hereinas from one endpoint to another endpoint or between two endpoints. Allranges disclosed herein are inclusive of the endpoints, unless specifiedotherwise.

Light detection devices includes front side illumination (FSI) imagesensors, back side illumination (BSI) image sensors, both having anarray of pixel sensors, or other suitable image sensor design. Achallenge of image sensors is cross-talk between adjacent lightdetection regions, or adjacent pixels. Optical cross-talk may occur whenphotons that are intended to be received by one light detection region,but end up being erroneously received by a neighboring light detectionregion. Such result may degrade the performance, for example, theresolution, of the image sensor. As image sensors become smaller andsmaller throughout development, the risk of cross-talk increasesaccordingly. Specifically, when a width of a pixel of an image sensorbecomes less than 1 micron, the risk of cross-talk significantlyincreases.

On the other hand, quantum efficiency (QE) is also a figure of merit asfar as an image sensor is concerned. Incident light may not penetratethrough metallic materials, or metallic material is opaque to photons.When metallic structure is presented in an image sensor, the photonimpinging to such metallic structure may not contribute to electrongenerated, and therefore the QE of such image sensor may be reduced.

The present disclosure provides an optical structure including a gridstructure to improve optical isolation between adjacent light detectionregions to alleviate cross-talk without considerably trading off quantumefficiency (QE).

Referring to FIG. 1A, FIG. 1A is a cross sectional view of an opticalstructure, according to some embodiments of present disclosure. Anoptical structure 1 at least includes a substrate 35 and a lightdetection region 61. The optical structure 1 may further include aprimary grid structure 130, a secondary grid structure 160, an isolationstructure 80, a lens 309, a color filter 170, and a light transmissionlayer 85.

In some embodiments, the substrate 35 is a p-type semiconductorsubstrate (P-Substrate) or an n-type semiconductor substrate(N-Substrate) comprising silicon. In some other alternative embodiments,the substrate 35 includes other elementary semiconductor, such asgermanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including silicon germanium(SiGe), gallium arsenide phosphide (GaAsP), aluminum indium arsenide(AlInAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide(InGaAs), indium gallium phosphide (InGaP), indium gallium arsenidephosphide (InGaAsP), combinations thereof, or the like. In some otherembodiments, the substrate 35 is a semiconductor on insulator (SOI). Insome other embodiments, the substrate 35 may include an epitaxial layer,a gradient semiconductor layer, and/or a semiconductor layer overlyinganother different type semiconductor layer, such as a silicon layer on asilicon germanium layer. The substrate 35 may or may not include dopedregions, such as a p-well, an n-well, or combination thereof.

The isolation structure 80 is in the substrate 35. In some embodiments,the isolation structure 80 may be a deep trench isolation (DTI), such asa backside deep trench isolation (BDTI). In some embodiments, theisolation structure 80 may include a dielectric material, which mayinclude oxide, nitride, or other suitable material that can be utilizedas an isolation feature. For example, the isolation structure 80 mayinclude silicon oxide (SiO₂), hafnium oxide (HfO₂), or the like. In someembodiments, a refractive index of the isolation structure 80 is lessthan a refractive index of silicon. In some embodiments, the isolationstructure 80 may optionally include a liner (not shown in FIG. 1A) at asidewall of the isolation structure 80 to alleviate cross-talk issue. Insome embodiments, the liner is a doped region surrounding the aforesaiddielectric material. The light detection region 61 is surrounded by theisolation structure 80 from a top view perspective. The light detectionregion 61 may include a light detection sensor, such as a pixel of apixel array, and a plurality of light detection regions 61 may bearranged in an array arrangement. In some embodiments, the pixel of thelight detection region 61 is a sub-micron level pixel which has a widthless than 1 micron.

The light transmission layer 85 is disposed over the substrate 35 andthe isolation structure 80. The light transmission layer 85 has a firstside 85 a opposite to the substrate 35 and a second side 85 b facing thesubstrate 35. The light transmission layer 85 may include oxidedielectric (such as silicon oxide, hafnium oxide, spin-on glass,fluoride-dopes silicate glass, undoped silica glass, or the like),antireflective coating (ARC), a multilayer structure of oxide dielectricand/or ARC, or the like. A material of the light transmission layer 85may, or may not be the same with a material of the dielectric materialof the isolation structure 80. For the sake of simplicity, only thelight detection region 61 (which can be deemed as a portion of a pixelarray region) is shown in FIG. 1A to FIG. 1C and FIG. 4 to FIG. 14. Insome embodiments, the substrate 35 further includes various regions,which may further include a periphery region (which may includenon-radiation-sensing devices, input/output circuitry, or logiccircuitry, etc.), a bonding pad region, and/or a scribe line region. Insome embodiments, the light detection sensor in the light detectionregion 61 is electrically connected to a bonding pad (not shown in FIG.1A), wherein the light detection region 61 and the bonding pad may be onthe second side 85 b of the light transmission layer 85 b, in some ofthe embodiments.

Referring to FIG. 1A, FIG. 2A, and FIG. 2B, FIG. 2A is a top viewperspective of an optical structure in one embodiment, FIG. 2B is a topview perspective of an optical structure in another embodiment. Aprimary grid structure 130 and a secondary grid structure 160 aredisposed above the first side 85 a of the light transmission layer 85.In some embodiments, the primary grid structure 130 is aligning abovethe isolation structure 80, and the secondary grid structure 160 islaterally surrounded by the primary grid structure 130. As shown in FIG.2A and FIG. 2B, the primary grid structure 130 and the secondary gridstructure 160 may have a circular shape or a tetragonal shape from a topview perspective. In some embodiments, the primary grid structure 130 isvertically aligned with the isolation structure 80, and a width Wa or adiameter Da of the primary grid structure 130 may be identical to orapproximate to a width or a diameter of a pixel of the light detectionregion 61 or a width or a diameter of the light detection region 61,which may be less than 1 micron. A separation Sa between an innersurface of the primary grid structure 130 and an outer surface of thesecondary grid structure 160 may be in a range from about 0.1 micron toabout 0.5 micron. The material of the primary grid structure 130 and thesecondary grid structure 160 will be subsequently discussed in FIG. 1Ato FIG. 1C. Although showing in a continuous circle or tetragonal shapein FIG. 2A and FIG. 2B, the primary and secondary grid structures may beof non-continuous patterns according to various designs. In some otherembodiments, the optical structure further includes a tertiary grid, aquaternary grid, a quinary grid . . . or the like. The number of gridsfor serving purpose(s) similar to the primary grid structure 130 and/orthe secondary grid structure 160 above the light detection region 61 isnot limited in the present disclosure. In some of the embodiments, thetertiary grid, the quaternary grid, or the quinary grid may besurrounded by the primary grid structure 130. For the purpose ofconciseness, the tertiary grid, the quaternary grid, the quinary grid,or the like, are not shown in FIG. 1A to FIG. 2B.

The color filter 170 is disposed over the first side 85 a of the lighttransmission layer 85, wherein the primary grid structure 130 and thesecondary grid structure 160 are in the color filter 170. The first side85 a of the light transmission layer 85 may directly contact the colorfilter 170. A certain frequency of light can pass through the colorfilter 170, for example, the color filter 170 can selectively pass anyone of the red, green, or blue (R/G/B) light toward the lighttransmission layer 85. In some embodiments, the color filters of aplurality of neighboring optical structures 1 are arranged in Bayerpattern, but the present disclosure is not limited thereto. In someembodiments, the color filter 170 may include organic dielectric, suchas polymer. In some embodiments, a thickness of the color filter 170 isidentical with a height of the primary grid structure 130. Alternativelyin some other embodiments, a thickness of the color filter 170 isgreater than a height of the primary grid structure 130. The opticalstructure 1 may further include a lens 309 above the color filter 170and aligning with a light detection region 61. The lens 309 faces thefirst side 85 a of the light transmission layer 85. In some embodiments,the lens 309 may be a condensing lens, which may have a semi-ellipsoid,a hemisphere shape, or other suitable shape. A size of the lens 309 maybe comparable to the size of the primary grid structure 130 from a topview perspective.

As shown in FIG. 1A, in some embodiments, the primary grid structure 130includes an oxide section 135 above the light transmission layer 85,which may include silicon oxide (SiO₂), hafnium oxide (HfO₂), or thelike. A refractive index of the oxide section 135 is less than arefractive index of the color filter 170. The oxide section 135 mayserve as a light guide due to the difference of the refractive indexbetween the oxide section 135 and the color filter 170. Specifically,reflection may occur when light 323 in the color filter 170 strikes aninner surface of the oxide section 135 (or a boundary between theprimary grid structure 130 and the color filter 170). Furthermore, theoxide section 135 has a lower light absorbance than metal, thus thequantum efficiency (QE) in current embodiment may be greater than acomparative embodiment where the primary grid structure is composed ofmetal. In some comparative embodiments where no secondary grid 160 ispresented, the light 323 with specific incident angle may reach and passthrough the light transmission layer 85, ending up in an adjacent lightdetection region 61, as demonstrated in dashed-dotted lines of FIG. 1A.

In some embodiments, the primary grid structure 130 may further includea antireflective coating (ARC) layer 198 above the oxide section 135,wherein the ARC layer 198 is vertically aligned with the oxide section135. In some embodiments, the primary grid structure 130 may furtherinclude a dielectric layer 100 surrounding the primary grid structure130. A material of the dielectric layer 100 may be identical with amaterial of the secondary grid structure 160, which will be subsequentlydiscussed in FIG. 12. In some alternative embodiments, the primary gridstructure 130 and/or the secondary grid structure 160 includes a singlematerial, such as a dielectric material, organic material, or metallicmaterial. In some embodiments, material of the primary grid structure130 may, or may not be identical with that of the secondary gridstructure 160.

Referring to FIG. 1B, FIG. 1B is a cross sectional view of an opticalstructure, according to some embodiments of present disclosure.Alternatively in some other embodiments, the primary grid structure 130is a composite grid structure, which includes a metal section, an oxidesection, and/or an organic section. For example, the composite gridstructure include a metal section 90 above the light transmission layer85, and an oxide section 135 above the metal section 90. The metalsection 90 may block light impinging thereon by absorbing the photon,therefore preventing the photon from traveling toward adjacent lightdetection regions 61. Alternatively stated, the metal section 90 maypossess the capability of alleviating the cross-talk issue better thanthat of the oxide section 135. In some embodiments, the metal section 90may include metal, such as copper, tungsten, aluminum copper, or thelike. However, the degradation of quantum efficiency (QE) of the opticalstructure 1 may exacerbate since the metal section 90 may have arelatively higher light absorbance. Therefore, a height of the metalsection 90 is limited to a certain extent to avoid significantdegradation of quantum efficiency (QE), and the oxide section 135 isdisposed above the metal section 90. Herein a refractive index of theoxide section 135 is lower than a refractive index of the color filter170 (which can also serve as a light guide, as previously discussed),and the oxide section 135 has a lower light absorbance than metal, thusthe degradation of quantum efficiency (QE) caused by the primary gridstructure 130 can be alleviated. The oxide section 135 may include oxidesuch as silicon oxide (SiO₂), hafnium oxide (HfO₂), or the like. It isnoteworthy that a refractive index of the metal section 90 is lower thana refractive index of the color filter 170, and the oxide section 135may also be replaced by any other suitable reflective material that hasa refractive index lower than a refractive index of the color filter170. In some embodiments, the composite grid structure may furtherinclude an ARC layer 198 over the oxide section 135 and/or a dielectriclayer 100 surrounding the primary grid structure 130. A material of thedielectric layer 100 may be identical with a material of the secondarygrid structure 160, which will be subsequently discussed.

Referring to FIG. 1C, FIG. 1C is a cross sectional view of an opticalstructure, according to some embodiments of present disclosure. In somealternative embodiments, the primary grid structure 130 and/or thesecondary grid structure 160 includes composite material, for example, acombination of dielectric material and metallic material, a combinationof organic material and metallic material, or the like. For example, thesecondary grid structure 160 includes two or more sections, such as afirst section 160A and a second section 160B different from the firstsection 160A as shown in FIG. 1C (wherein the sections are collectivelyreferred to as the secondary grid structure 160).

Referring to FIG. 1A, FIG. 1B and FIG. 1C, the secondary grid structure160 surrounded by the primary grid structure 130 is disposed above thefirst side 85 a of the light transmission layer 85 to further alleviatecross-talk issue, wherein the secondary grid structure 160 overlaps withthe light detection region 61 from top view perspective, and the primarygrid structure 130 is closer to the isolation structure 80 than thesecondary grid 160. Specifically, there's a risk of light 323 passingthrough the light transmission layer 85 between the primary gridstructure 130 and the isolation structure 80, and thereby erroneouslyreceived by adjacent light detection region 61 (as shown as adashed-dotted line in FIG. 1A, FIG. 1B and FIG. 1C). In order to hinderlight 323 from being erroneously received by adjacent light detectionregion 61, the secondary grid structure 160 has a refractive index ofthe secondary grid structure 160 is less than a refractive index of thecolor filter 170. The secondary grid structure 160 may serve as a lightguide due to the difference of the refractive index between thesecondary grid structure 160 and the color filter 170. In someembodiments, the light 323 reflected off the secondary grid structure160 may be guided to the intended light detection region 61.Specifically, reflection may occur when light in the color filter 170strikes a boundary between the secondary grid structure 160 and thecolor filter 170. Furthermore, the secondary grid structure 160 has alower light absorbance than metal, thus the degradation of quantumefficiency (QE) caused by the secondary grid structure 160 can bealleviated. In some embodiments, the secondary grid structure 160 is adielectric grid structure, such as an oxide grid, or other suitable lowrefractive index grid. For example, the secondary grid structure 160 mayinclude silicon oxide (SiO₂), hafnium oxide (HfO₂), or the like. In someembodiments, a height of the secondary grid structure 160 is less than aheight of the primary grid structure 130, since it may not require aheight of the secondary grid structure 160 to be identical with a heightof the primary grid structure 130 to effectively hinder the light 323from passing through the light transmission layer 85 between the primarygrid structure 130 and the isolation structure 80, and on the otherhand, may instead cause degradation of quantum efficiency (QE).

In some of the embodiments, the effectiveness of color filter 170 withregard to filtering the certain frequency of light may be affected bythe incorporation of the secondary grid structure 160 due to thedecreased amount of the color filter 170. Therefore in some embodiments,the height of the secondary grid structure 160 may be less than 0.5micron (or in some embodiments from about 0.1 micron to about 0.5micron), while a thickness of the color filter 170 and a height of theprimary grid structure 130 may be added in accordance with the height ofthe secondary grid structure 160 to compensate the deceasedeffectiveness of color filter 170 stems from the incorporation of thesecondary grid structure 160. Alternatively stated, in some embodiments,the thickness of the color filter is associated with the height of thesecondary grid in a sense that compared to the embodiment where nosecondary grid is presented, the thickness of the color filter incurrent embodiment may be greater than the one without secondary grid.For example, the thickness of the color filter in current embodiment maybe greater than the thickness of the color filter without secondary gridby the thickness of the secondary grid. The excess thickness in currentembodiment may compensate the deficient color filtering efficiencyresulted from the presence of the secondary grid.

Referring to FIG. 3A, FIG. 3A shows a flow chart representing a methodfor fabricating an optical structure, in accordance with someembodiments of the present disclosure. The method 1000 for fabricatingan optical structure includes providing a substrate (operation 1001,which can be referred to FIG. 4), forming a light detection region inthe substrate (operation 1003, which can be referred to FIG. 4), formingan isolation structure surrounding the light detection region (operation1005, which can be referred to FIG. 4), forming a primary grid over theisolation structure (operation 1008, which can be referred to FIG. 6 toFIG. 7), and forming a secondary grid surrounded by the primary grid(operation 1111, which can be referred to FIG. 8 to FIG. 12).

Referring to FIG. 3B, FIG. 3B shows a flow chart representing a methodfor fabricating an optical structure, in accordance with someembodiments of the present disclosure. The method 2000 for fabricatingan optical structure includes providing a substrate (operation 2001,which can be referred to FIG. 4), forming a light detection region inthe substrate (operation 2002, which can be referred to FIG. 4), formingan isolation structure surrounding the light detection region (operation2004, which can be referred to FIG. 4), forming a metal layer over thesubstrate (operation 2007, which can be referred to FIG. 5), forming afirst dielectric layer over the metal layer (operation 2009, which canbe referred to FIG. 6), patterning the metal layer and the firstdielectric layer (operation 2011, which can be referred to FIG. 7),forming a second dielectric layer over the substrate (operation 2013,which can be referred to FIG. 8), patterning the second dielectric layerby a first mask to form a trench (operation 2016, which can be referredto FIG. 9), and patterning the second dielectric layer by a second maskdifferent from the first mask (operation 2018, which can be referred toFIG. 10 to FIG. 12).

Referring to FIG. 4, FIG. 4 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. A substrate 35 aspreviously discussed in FIG. 1A is provided, and at least one lightdetection region 61 as well as an isolation structure 80 surrounding alight detection region 61 from a top view perspective are formed in thesubstrate 35. The light detection region 61 may be formed by disposing alight detection sensor in the substrate 35, wherein the light detectionsensor can be an optical pixel, or the like. In some embodiments, theoptical pixel (not shown in FIG. 4) of the light detection region 61 isa sub-micron level pixel which has a width less than 1 micron.

The isolation structure 80 is formed in the substrate 35. In someembodiments, the isolation structure 80 may be a deep trench isolation(DTI), such as a backside deep trench isolation (BDTI). In someembodiments, the isolation structure 80 is formed by forming a deeptrench, performing a plasma diffusion operation involvingplasma-immersion ion implantation to form a doped trench linersurrounding the deep trench, subsequently depositing a dielectricmaterial (such as an oxide material or a nitride material, for examplesilicon oxide (SiO₂), hafnium oxide (HfO₂), or the like) in the deeptrench, and thereafter removing a portion of the dielectric materialoutside of the deep trench by performing a chemical mechanicalplanarization (CMP) operation. The deep trench may be formed by etchingoperations (wet etching or dry etching) or photolithography patterningfollowed by reactive ion etching (RIE); and the deposition of thedielectric material may involve a variety of techniques, such aschemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), atmospheric pressure chemical vapor deposition(APCVD), low-pressure CVD (LPCVD), high density plasma CVD (HDPCVD),atomic layer CVD (ALCVD), sub-atmospheric CVD (SACVD), physical vapordeposition (PVD), atomic layer deposition (ALD), sputtering, and/orother suitable operations. It is noteworthy that a refractive index ofthe isolation structure 80 may be less than a refractive index ofsilicon.

Subsequently, the light transmission layer 85 is formed over thesubstrate 35 and the isolation structure 80. The light transmissionlayer 85 may include oxide dielectric (such as silicon oxide, hafniumoxide, spin-on glass, fluoride-dopes silicate glass, undoped silicaglass, or the like), antireflective coating (ARC), a multilayerstructure of oxide dielectric and/or ARC, or the like. The lighttransmission layer 85 may be formed by a variety of techniques, such aschemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), atmospheric pressure chemical vapor deposition(APCVD), low-pressure CVD (LPCVD), high density plasma CVD (HDPCVD),atomic layer CVD (ALCVD), sub-atmospheric CVD (SACVD), coating, spin-on,sputtering, and/or other suitable operations.

Referring to FIG. 5, FIG. 5 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Optionally, a metallayer 90′ is subsequently formed above the light transmission layer 85when a composite grid is to be formed. The metal layer 90′ may includemetal, such as copper, tungsten, aluminum copper, or the like.

Referring to FIG. 6, FIG. 6 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. A first dielectriclayer 135′ is formed over the light transmission layer 85, or over themetal layer 90′ if the metal layer 90′ was previously formed above thelight transmission layer 85. The first dielectric layer 135′ may includeoxide, such as silicon oxide (SiO₂), hafnium oxide (HfO₂), or the like.In some other embodiments, the first dielectric layer 135′ may includeorganic material. An antireflective coating (ARC) layer 198 is formedabove the first dielectric layer 135′, and a photomask 1989 is formedabove the antireflective coating (ARC) layer 198. The first dielectriclayer 135′ may be formed by a variety of techniques, such as chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), plasma-enhanced chemical vapor deposition (PECVD),atmospheric pressure chemical vapor deposition (APCVD), low-pressure CVD(LPCVD), high density plasma CVD (HDPCVD), atomic layer CVD (ALCVD),sub-atmospheric CVD (SACVD), and/or other suitable operations. Theantireflective coating (ARC) layer 198 may be formed by a variety oftechniques, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), plasma-enhancedchemical vapor deposition (PECVD), atmospheric pressure chemical vapordeposition (APCVD), low-pressure CVD (LPCVD), high density plasma CVD(HDPCVD), atomic layer CVD (ALCVD), sub-atmospheric CVD (SACVD), and/orother suitable operations.

Referring to FIG. 7, FIG. 7 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently aphotolithography operation is performed, wherein the metal layer 90′,the first dielectric layer 135′, and the antireflective coating (ARC)layer 198 are patterned by the photomask 1989. Specifically, the metallayer 90′ and the first dielectric layer 135′ are patterned into themetal section 90 and the oxide section 135 respectively. It should benoted that the metal section 90 and the oxide section 135 may have acircular shape or a tetragonal shape from a top view perspective, whichwas previously discussed in FIG. 1A to FIG. 2B. Furthermore, the metalsection 90 and the oxide section 135 (which would become a portion ofthe primary grid 130 subsequently) are vertically aligned with theisolation structure 80 in order to improve the alignment between anarrangement of each of the light detection region 61 and an arrangementof the corresponding oxide section 135 and/or the corresponding metalsection 90. The photomask 1989 is subsequently removed.

Referring to FIG. 8, FIG. 8 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. A second dielectriclayer 100′ is formed above the light transmission layer 85. Thereby themetal section 90, the oxide section 135, and the ARC layer 198 areinside the second dielectric layer 100′ and surrounded by the seconddielectric layer 100′. The second dielectric layer 100′ may includeoxide, such as silicon oxide (SiO₂), hafnium oxide (HfO₂), or the like.In some embodiments, a top surface of the second dielectric layer 100′may be above a top surface of the ARC layer 198. Subsequently, a firstmask 201 is formed above the second dielectric layer 100′.

Referring to FIG. 9, FIG. 9 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently, atrench 319 is formed by patterning the second dielectric layer 100′using the first mask 201. A bottom surface of the trench 319 is above atop surface of the light transmission layer 85. The trench 319 islaterally surrounded by the oxide section 135, and the trench 319overlaps with the light detection region 61 from top view perspective.In some embodiments, a distance Sa′ between an inner surface 135 i ofthe oxide section 135 and a sidewall of the trench 319 is in a rangefrom about 0.1 micron to about 0.5 micron. The distance may bepredetermined based on various dimensional considerations, including,but not limited to, the final height and width of the secondary grid,the concentrating ability of the lens, and the like.

Referring to FIG. 10, FIG. 10 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently, afilling material 329, for example, a photoresist, is filled in thetrench 319. It is noteworthy that a distance is between a bottom surfaceof the filling material 329 and the top surface of the lighttransmission layer 85. An excess amount of the filling material 329outside of the trench 319 and the first mask 201 are subsequentlyremoved.

Referring to FIG. 11, FIG. 11 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently asecond mask 202 different from the first mask 201 is disposed above thesecond dielectric layer 100′, and a photolithography operation isperformed to pattern the second dielectric layer 100′. Specifically, aportion of the second dielectric layer 100′ not covered by the fillingmaterial 329 and the second mask 202 is removed by the photolithographyoperation. Alternatively stated, a portion of the second dielectriclayer 100′ below the filling material 329 (referring to FIG. 10) and aportion of the second dielectric layer 100′ covered by the second mask202 (referring to FIG. 10) are remained. In some embodiments, a width ofthe second mask 202 is greater than a width of each of the metal section90, the oxide section 135, and the ARC layer 198. Thereby the metalsection 90, the oxide section 135, and the ARC layer 198 are surroundedby the remaining portion of the second dielectric layer 100′ covered bythe second mask 202, and such remaining portion of the second dielectriclayer 100′ are hereinafter denoted as a dielectric layer 100.

Referring to FIG. 12, FIG. 12 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently thefilling material 329 and the second mask 202 are removed. The remainingportion of the second dielectric layer 100′ which was previously coveredby the filling material 329 constitutes the secondary grid structure160. It should be noted that a material of the secondary grid 160 may beidentical with a material of the second dielectric layer 100′. In somealternative embodiments, other materials may be additionally depositedso that the secondary grid structure 160 includes composite material,for example, a combination of dielectric material and metallic material,a combination of organic material and metallic material, or the like.Furthermore, hereinafter the patterned metal section 90, the oxidesection 135, the ARC layer 198 and the dielectric layer 100 arecollectively denoted as the primary grid structure 130. Herein a heightof the primary grid structure 130 is greater than a height of thesecondary grid structure 160, while a separation Sa between an innersurface of the primary grid structure 130 and an outer surface of thesecondary grid structure 160 may be in a range from about 0.1 micron toabout 0.5 micron. In some embodiments, the height of the secondary gridstructure 160 may be less than 0.5 micron (or in some embodiments fromabout 0.1 micron to about 0.5 micron). From a top view perspective, thesecondary grid structure 160 is surrounded by the primary grid structure130, as previously discussed and shown in FIG. 2A and FIG. 2B.

Referring to FIG. 13, FIG. 13 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. Subsequently thecolor filter 170 is formed over the light transmission layer 85, whereinthe primary grid structure 130 and the secondary grid structure 160 arein the color filter 170. In some embodiments, the color filter 170 mayinclude organic dielectric, such as polymer. Herein a refractive indexof the color filter 170 is greater than a refractive index of thesecondary grid structure 160 and a refractive index of the primary gridstructure 130 (at least the oxide section 135 of the primary gridstructure 130 and the metal section 90 if it is previously formed). Insome embodiments, a thickness of the color filter 170 is identical witha height of the primary grid structure 130. Alternatively in some otherembodiments, a thickness of the color filter 170 is greater than aheight of the primary grid structure 130. In some embodiments, thethickness of the color filter is associated with the height of thesecondary grid in a sense that compared to the embodiment where nosecondary grid is presented, the thickness of the color filter incurrent embodiment may be greater than the one without secondary grid.For example, the thickness of the color filter in current embodiment maybe greater than the thickness of the color filter without secondary gridby the thickness of the secondary grid. The excess thickness in currentembodiment may compensate the deficient color filtering efficiencyresulted from the presence of the secondary grid.

Referring to FIG. 14, FIG. 14 is a cross sectional view of an opticalstructure during intermediate stages of manufacturing operations,according to some embodiments of present disclosure. A lens 309 isformed above the color filter 170 and aligning with the light detectionregion 61. In some embodiments, the lens 309 may be a condensing lens,which may have a semi-ellipsoid, a hemisphere shape, or other suitableshape. A size of the lens 309 may be comparable to the size of theprimary grid structure 130 from a top view perspective.

In some embodiments, a bonding pad and/or a solder bump (not shown inFIG. 14) may be formed on a side 35 b of the substrate 35, wherein theside 35 b faces away from the light transmission layer 85. The bondingpad and/or the solder bump may be electrically connected to a pixelformed in the light detection region 61 through a redistribution layer(RDL), and/or a conductive via. In some embodiments, the light detectionregion 61 is connected to a periphery region, which may includenon-radiation-sensing devices, input/output circuitry, or logiccircuitry, etc. In some embodiments, a portion of the substrate 35 issingulated by sawing through scribe regions (not shown in FIG. 14)surrounding the optical structure 1.

The present disclosure provides an optical structure including a primarygrid structure 130 and a secondary grid structure 160 surrounded by theprimary grid structure 130 to alleviate cross-talk issue withoutconsiderably trading off quantum efficiency (QE). Generally, when awidth of a pixel in a light detection region becomes less than 1 micron,the risk of cross-talk significantly increases. Specifically, thesecondary grid structure 160 may hinder the light from passing through aseparation between the primary grid structure 130 and the isolationstructure 80 to an extent. The secondary grid structure 160 a materialhaving a lower refractive index than the surrounding color filter 170,thus the secondary grid structure 160 may reflect light in the colorfilter 170 by inducing reflection, thereby the reflected light may beguided to the intended light detection region 61, instead of erroneouslydirected to an adjacent light detection region 61. Furthermore, bypatterning the second dielectric layer 100′ by a first mask 201 to forma trench 319 and patterning the second dielectric layer 100′ by a secondmask 202 different from the first mask 201, the accuracy of positioningthe secondary grid structure 160 may be improved.

Some embodiments of the present disclosure provide an optical structure,including a substrate, a light detection region in the substrate, anisolation structure in the substrate, surrounding the light detectionregion, a color filter layer over the substrate, and a dielectric gridstructure in the color filter layer, the dielectric grid structureoverlapping with the light detection region.

Some embodiments of the present disclosure provide an optical structure,including a substrate, a light detection region in the substrate, anisolation structure in the substrate defining the light detectionregion, a dielectric layer over the substrate, and a grid structure inthe dielectric layer, wherein a first refractive index of the dielectriclayer is greater than a second refractive index of the grid structure,and wherein more than one grid are overlapping with the light detectionregion.

Some embodiments of the present disclosure provide a method forfabricating an optical structure, including providing a substrate,forming a light detection region in the substrate, forming an isolationstructure surrounding the light detection region, and forming a gridstructure over the isolation structure, wherein forming the gridstructure comprises, forming a primary grid over the isolationstructure, and forming a secondary grid surrounded by the primary gridsubsequent to forming the primary grid.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother operations and structures for carrying out the same purposesand/or achieving the same advantages of the embodiments introducedherein. Those skilled in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method for fabricating an optical structure,comprising: forming a light detection region in a substrate; forming anisolation structure at surrounding the light detection region; andforming a primary grid over the isolation structure, comprising: forminga metal layer over the isolation structure; forming a first dielectriclayer over the metal layer; and partially removing the metal layer andthe first dielectric layer with a first mask by patterning; and forminga secondary grid at least partially surrounded by the primary gridlaterally.
 2. The method of claim 1, wherein forming the secondary gridcomprises: forming a second dielectric layer over the substrate;patterning the second dielectric layer by a second mask to form atrench.
 3. The method of claim 2, wherein forming the secondary gridfurther comprising: filling the trench with photoresist material afterpatterning the second dielectric layer.
 4. The method of claim 2,further comprising forming a color filter layer over the substrate afterpatterning the second dielectric layer.
 5. The method of claim 1,further comprising forming a liner lining at a sidewall of the primarygrid.
 6. The method of claim 5, wherein the liner is free from being indirect contact with the secondary grid.
 7. The method of claim 4,wherein a total thickness of the color filter is greater than a totalheight of the secondary grid.
 8. A method for fabricating an opticalstructure, comprising: forming a light detection region in a substrate;forming an isolation structure surrounding the light detection region;and forming a primary grid over the isolation structure, comprising:forming a metal layer over the isolation structure; forming a firstdielectric layer over the metal layer; and patterning the metal layerand the first dielectric layer; forming a second dielectric layer overthe primary grid; forming a trench in the second dielectric layer;forming a filling material in the trench; and forming a secondary gridat least partially surrounded by the primary grid laterally, comprising:partially removing the second dielectric layer by patterning, thereby atleast a portion of the filling material and a portion of the seconddielectric layer below the filling material is remained.
 9. The methodof claim 8, wherein forming the secondary grid further comprisesremoving the filling material to expose at least a portion of the seconddielectric layer.
 10. The method of claim 9, further comprising forminga color filter over the exposed portion of the second dielectric layer.11. The method of claim 8, further comprising forming a liner lining ata sidewall of the primary grid.
 12. The method of claim 11, wherein theliner is free from being in direct contact with the secondary grid. 13.The method of claim 10, further comprising forming a lens over the colorfilter.
 14. A method for fabricating an optical structure, comprising:forming a light detection region in a substrate; forming an isolationstructure surrounding the light detection region; and forming a primarygrid over the isolation structure, comprising: forming a metal layerover the isolation structure; forming a first dielectric layer over themetal layer; forming an antireflective coating (ARC) layer over thefirst dielectric layer; and patterning the metal layer, the firstdielectric layer, and the ARC layer; and forming a secondary grid atleast partially surrounded by the primary grid laterally.
 15. The methodof claim 14, further comprising forming a second dielectric layer overthe substrate, wherein a top surface of the ARC layer is below a topsurface of the second dielectric layer.
 16. The method of claim 15,wherein forming the secondary grid further comprises: forming a trenchin the second dielectric layer.
 17. The method of claim 16, whereinforming the secondary grid further comprises: forming a filling materialin the trench.
 18. The method of claim 17, wherein forming the secondarygrid further comprises: partially removing the second dielectric layerby patterning, thereby at least a portion of the filling material and aportion of the second dielectric layer below the filling material isremained.
 19. The method of claim 18, wherein forming the secondary gridfurther comprises: removing the filling material.
 20. The method ofclaim 14, further comprising forming a liner in direct contact with theARC layer.